Description
This diagnostic monitors the operation of the air/fuel ratio feedback controls. In order to provide the best possible combination of driveability, fuel economy, and emission control, the powertrain control module (PCM) uses a Closed Loop air/fuel metering system. The PCM monitors the heated oxygen sensor (HO2S) input and, when in Closed Loop, adjusts the fuel delivery based on the HO2S information. Changes in fuel delivery will be indicated by the long term and the short term fuel trim values that are displayed on the scan tool. The ideal fuel trim value is around 0 percent. The PCM will add fuel when the heated oxygen sensor signal is indicating a lean condition. Additional fuel is indicated by fuel trim values that are more than 0 percent. The PCM will reduce the amount of fuel delivered when a rich condition is indicated by the HO2S. Fuel trim values less than 0 percent indicate a reduction in fuel. If the PCM detects that the long term fuel trim is below a predetermined value, this DTC sets.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC P0172 HO2S Fuel Trim System Rich Bank 1 |
| • | DTC P0175 HO2S Fuel Trim System Rich Bank 2 |
HO2S Indication | Short Term FT Action | Long Term FT Action | Short Term FT Response |
|---|---|---|---|
Lean Condition | Quick Increase of 1% or More | Slow Increase of 1% or More | Return to 0% |
Desired Condition | Stays Near 0% | Stays at Learned +/- Value | Stays Near 0% |
Rich Condition | Quick Decrease of -1% or Less | Slow Decrease of -1% or Less | Return to 0% |
Conditions for Running the DTC
| • | Before the PCM can report that DTC P0172 or P0175 failed, DTC P0442 must run and pass. |
| • | DTCs P0030, P0050, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0135, P0155, P0300-P0306, P0335, P0339, P0401, P0404, P0442, P0443, P0496, P1128, P1129, P2227, P2228, P2229, P2413, P2414, and P2415 are not set. |
| • | Engine coolant temperature (ECT) at least 69°C (156°F). |
| • | Intake air temperature (IAT) is at least 0°C (32°F). |
| • | Manifold absolute pressure (MAP) is at least 24 kPa. |
| • | Engine speed is between 630-4,000 RPM. |
| • | The engine is operating in Closed Loop. |
| • | The evaporative emission (EVAP) monitor is not running. |
| • | DTC P0172 and DTC P0175 run once per drive cycle when the above conditions are met. |
Conditions for Setting the DTC
The long term fuel trim of bank 1 or bank 2 is less than -16 percent.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Use a scan tool in order to clear the MIL and the DTC. |
Diagnostic Aids
Check for any of the following conditions:
| • | Inspect for a restriction in the inlet air passage--A duct or inlet hose that collapses when hot or that is blocked by debris. |
| • | Test for the correct fuel pressure--The fuel system will be rich if the fuel pressure is too high. In order to determine the cause of DTC P0172 or DTC P0175 monitoring the fuel pressure while driving the vehicle at various road speeds may be necessary. Refer to Fuel System Diagnosis . |
| • | Inspect for a damaged wiring harness--Inspect the wiring harness for damage. If the harness appears to be OK, observe the heated oxygen sensor (HO2S) bank 1 or bank 2 sensor 1 display on the scan tool while moving the connectors and the wiring harnesses related to the sensor. A change in the display will indicate the location of the fault. |
| • | Inspect for a contaminated oxygen sensor. readings. If contamination is found, determine the cause and correct the condition before replacing the HO2S. |
| • | Inspect the HO2S bank 1 or bank 2 sensor 1 for water intrusion into the wiring harness and the sensor housing. Water can create a short to voltage in the HO2S signal circuit causing a false rich indication. |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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The Diagnostic System Check - Vehicle prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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This step determines whether a condition exists.
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If DTC P0172 and P0175 are set at the same time, this indicates both banks of the engine are operating rich. Inspect the items that would cause both banks to operate rich.
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This step tests for excess fuel from a fuel injector. The fault may be a fuel injector or the fuel injector electrical circuit.
Step | Action | Value(s) | Yes | No | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | ||||||||||||||||||||
|
Important: If any DTCs are set, except P0172 and P0175, refer to those DTCs before proceeding with this diagnostic.
Does the scan tool display more than the specified value? | -16% | Go to Step 3 | Go to Step 4 | |||||||||||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||||||||||||
Are both banks of the engine operating rich? | Go to Step 5 | Go to Step 6 | ||||||||||||||||||||
5 | Visually and physically inspect for any of the following conditions:
Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7 | ||||||||||||||||||
Visually and physically inspect for any of the following conditions:
Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7 | |||||||||||||||||||
7 | Test for an intermittent and for a poor connection at the appropriate heated oxygen sensor (HO2S). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 8 | ||||||||||||||||||
8 | Replace the HO2S. Refer to the appropriate procedure: Did you complete the replacement? | -- | Go to Step 9 | -- | ||||||||||||||||||
9 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 10 | ||||||||||||||||||
10 | In order to ensure that the performance of the catalyst has not been affected by the fault that set this DTC, operate the vehicle within the conditions for running and setting DTC P0420/0430 and verify that DTC P0420/0430 runs and passes. Refer to DTC P0420 or P0430 . Does the DTC run and pass? | -- | Go to Step 11 | Go to DTC P0420 or P0430 | ||||||||||||||||||
11 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
